Full wave rectifier assemblies have long been employed with rotary electric machines as, for example, alternators. In many cases, for any of a variety of reasons, it is desirable that such machines be of the so-called "brushless" variety. Where such is desired, it is necessary that the magnetic field be produced in the rotor so that induced current may be taken from stator windings, thereby eliminating the need for brushes in the electrical circuit for the induced current.
This in turn requires that the means for producing the magnetic field be carried by the rotor. This can, of course, be accomplished through the use of permanent magnets, but where the machine is to be of relatively high capacity, the necessarily more intense magnetic field is provided by directing direct current through windings carried by the rotor. To provide such current to rotor windings and yet omit brushes, it therefore becomes necessary to generate electric current for energizing the rotor windings within the rotor itself, that is, by means of a so-called "exciter".
In the usual case, the exciter includes a stationary magnet stator and the same induces the exciter current in additional windings carried by the rotor. Conveniently, the arrangement is one of an alternator with the result that alternating current is generated. In order to provide a direct current to the rotor windings, it is necessary that the alternating current be rectified. And again, to avoid the use of brushes, the rectifier for performing such an operation must be carried by the rotor.
Over the years, a variety of rectifier assemblies to be carried by rotors have been developed. Examples are shown in U.S. Pat. Nos. 3,368,091 issued Feb. 6, 1968 to Layman; 3,412,271 issued Nov. 19, 1968 to Hall; and 3,739,209 issued June 12, 1973 to Drabik. One necessary characteristic of such assemblies is that they be able to withstand the high stresses imposed upon them by centrifugal force during rotor rotation. Another characteristic required of such rectifier assemblies is that they be as compact as possible. This is necessary since they are carried by the rotor, and any unnecessary increase in rotor size is undesirable since (a) it will necessarily increase the size of the stator, and thus the size of the overall machine, and (b) an increase in size will quite likely result in an increase in mass with the larger mass of the rotor increasing the stresses present during operation.
Heretofore, when it has been attempted to make a rectifier assembly axially compact, it has generally been accomplished at the expense of an increase in the radial dimension of the assembly. This in turn has generally resulted in rectifier assembly components being located a greater distance from the axis of rotation than is desirable, with the consequence that, for a given rotor speed, the centripetal velocity of such components is greater than would be the case if they were located more radially inwardly. As an ultimate result, such radially outwardly located components are subject to greater stresses induced by centrifugal force. The rectifier assemblies illustrated in the previously identified Layman and Drabik patents are subject to this difficulty.
Conversely, when it it has been attempted to avoid the problems imposed by such structures by making the assembly radially compact as, for example, illustrated in the previously identified Hall patent, such is accomplished at the expense of an increased axial dimension. As can be appreciated from the illustration in the Hall patent, this in turn requires either a radial or an axial increase in that portion of the rotor in which the magnetic field is generated or a reduction in the amount of magnetic material that can be carried by the rotor, and thus a decrease in generating efficiency.
The present invention is directed to overcoming one or more of the above problems.